In the field of secure access to a determined space such as vehicles, it is known to use an entry system for the vehicles using a smart key for wireless transmission of commands. By means of the access system, it is possible to authorise access to this space to a person wearing a personalised wearable object such as an electronic key on the basis of a check or authentication of the personalised electronic key. An interrogation signal can firstly be transmitted from an access authorisation or unlocking device of the vehicle to the personalised electronic key. As soon as this interrogation signal is received, the electronic key can be activated and a calculation of a response signal is conducted in said electronic key before a coded transmission to the access authorisation device of the vehicle. A control is subsequently conducted in the access device of the vehicle to determine whether the key is properly recognised for opening of said vehicle.
For control of access to a vehicle, for example, by means of an electronic smart key, the unlocking device of the vehicle can firstly be activated by a mechanical action, for example, on the door handle of the vehicle. From this moment, the unlocking device transmits a coded interrogation signal, which is received by the electronic key to activate it. The electronic key can be supplied with power by its own energy source such as a battery. In general, this interrogation signal is transmitted from the vehicle at a low carrier frequency, whereas the coded response signal of the electronic key is transmitted at a high carrier frequency.
The electronic key comprises a processing unit or a digital processing unit, which is connected to storage devices in which an encryption algorithm and/or an identification code for access to the vehicle, for example, are stored. Once activated by the interrogation code signal, the electronic key transmits its coded identification signal to the vehicle for a command for locking or unlocking parts or functions of the vehicle.
To facilitate access to the vehicle without having to handle the electronic key, an electronic key has already been proposed, from which a response signal is automatically transmitted to the vehicle in accordance with an interrogation signal received from the vehicle. For this, the key must be located in a confined area around the vehicle to be able to receive this interrogation signal coming from the vehicle. Moreover, the key only transmits a response signal to the vehicle if the interrogation signal has been recognised by the key. This response signal thus allows the command for locking and unlocking parts or functions of the vehicle.
The reception limits of the signals are determined by the propagation characteristics of the radiofrequency signals used for the exchanges of information and by the characteristics of the power transmitted and sensitivity of the transmitter-receivers used in the vehicle and in the key. The confined zone around the vehicle is generally defined by a threshold of minimum power received.
With such an electronic key automatically controlled by the interrogation signal coming from the vehicle there is a risk of allowing the vehicle, to be opened by means of intermediate relays without the knowledge of the wearer of the electronic key. This provides ill-intentioned persons with the ability to use these intermediate relays between the vehicle and the wearer of the electronic key to open the vehicle and start it. These relays are capable of reproducing the coded interrogation signal or coded response signal going to the key or to the vehicle respectively, each of which signals comprise a sequence of binary data.
A first intermediate relay of a first ill-intentioned person is close to the vehicle to receive an interrogation signal from the vehicle. This interrogation signal is converted into a radiofrequency signal for transmission to a second intermediate relay of a second ill-intentioned person located close to the wearer of the personalised electronic key for the vehicle to be opened and started. The second intermediate relay once again converts the radiofrequency signal of the first intermediate relay into a new interrogation signal at low frequency. The personalised electronic key worn by the person authorised to access the vehicle receives the new interrogation signal and after recognition of this interrogation signal transmits a coded identification response signal at high frequency. This radiofrequency response signal of the electronic key can be received directly by the unlocking device of the vehicle if the distance from the vehicle is short, e.g. less than 50 m. However, if the distance between the electronic key and the vehicle is much greater, e.g. more than 1 km, there must be a further exchange of radiofrequency signals from the key and via the two intermediate relays to the vehicle.
The secure access systems known from the art encounter several problems to ensure that the vehicle is opened solely by the personalised electronic key. In particular, it is generally difficult to determine the distance separating the electronic key and the vehicle to authorise opening of the vehicle only by the electronic key at a short distance from the vehicle. This constitutes a disadvantage of the secure access systems of the prior art.
Patent EP 673 003 B1 describes a system for secure access to a vehicle by means of an electronic key. Following action on the handle of the vehicle, the unlocking device of the vehicle transmits a coded interrogation signal for the key, which receives it and transmits a coded response signal to the unlocking device. In the case where the response code transmitted by the key coincides with a reference code of the unlocking device, authorisation for access to the vehicle is effected. A distance detection device is also provided to measure the distance between the key and the vehicle to enable the key to transmit the response code only in the vicinity of the vehicle. Such a secure access system does not eliminate the possibility of unauthorised opening of the vehicle by intermediate relays, which constitutes a disadvantage.
U.S. Pat. No. 6,538,560 B1 describes a system for access to an unlocking device of a vehicle by means of an electronic transponder key. The device of the vehicle transmits a coded signal at low frequency to activate the electronic key and allow it to activate its transmitter and receiver unit at high frequency. A high-frequency coded interrogation signal is then transmitted and received by the key, which must check its validity. Processing of the low-frequency coded signal is conducted in the key to allow transmission of a coded response signal at high frequency, taking into account the identification of the transmitter. The device of the vehicle receives the high-frequency coded signal from the key to check its validity and authorise access to the vehicle upon affirmation. Processing of the coded signal received from the unlocking device of the vehicle must be conducted in the key, which requires complicated circuitry in the key and increases the power consumption of the battery-supplied key, which constitutes a disadvantage.
In the prior art, it is also known to use a UWB communication system to authorise access to a vehicle by an electronic smart key. With this type of UWB communication, the flight time of the signals from the vehicle to the key and from the key to the vehicle, and therefore the distance between these two entities, is determined precisely. In contrast, this type of radiofrequency link also involves the use of a digital signal processing (DSP) microprocessor both in the unlocking device of the vehicle and in the electronic key. This requires a complex technology and therefore a high electrical energy consumption. Therefore, this constitutes a disadvantage of such an access system. Moreover, in such a system the distance measurement phase is generally distinguished from the authentication phase and this allows a potential attack, in which only the distance measurement phase could be hacked.